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Ask Phil Your Own Question
Phil, Mechanical Engineer
Category: HVAC
Satisfied Customers: 6022
Experience:  Retired HVAC/ Electrical & Boiler contractor. Industrial
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Still there?
My shower won't trigger our boiler. Just

Customer Question

Customer: Hi - still there?
My shower won't trigger our boiler. Just happened today. Water pressure to the shower is good and bathroom taps are fine.
JA: Thanks. Can you give me any more details about your issue?
Customer: I was trying to recalibrate the thermostat on the mixer tap on the shower - that's when the hot water stopped
it's a vaillant combi boiler
no other problems
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Submitted: 1 year ago.
Category: HVAC
Expert:  Andrew Smith replied 1 year ago.

Can you tell me if it improves if you turn the hot water temperature down on the boiler so you have to run the hot water faster?

Is it only on the shower?

Customer: replied 1 year ago.
Only the shower yes.Have turned water temp down to 42c but boiler still not firing
Customer: replied 1 year ago.
A bit more info:Shower was working fine earlier but thermostat on mixer was a bit cold. Followed instructions to recalibrate the temperature and since then it's only run cold.
Expert:  Andrew Smith replied 1 year ago.

The diaphragm in the boiler will have stretched so it takes more water flow through the boiler to fire it.

The problem with a thermostatic shower is that it throttles down the hot water to get to the correct temperature, at the moment that takes it below the minimum flow rate to fire the boiler.

It will get better if you fit a new diaphragm in the valve.

Customer: replied 1 year ago.
Will recalibrating the thermostat have caused that to happen? It literally happened immediately when I started going through the process.
Expert:  Andrew Smith replied 1 year ago.

Yes, it will affect the flow rate.

This is why I said turn down the hot water temperature on the boiler to see if it will fire due to a faster hot water flow rate